1. Field of the Invention
The present invention relates to a structure for reflecting light, which reflects light within at least any one wave length range of a visible ray range, an infrared ray range and an ultraviolet ray range based on diffraction and scattering actions of light. Moreover, this invention relates to a structure for reflecting light and a product adopting the structure for reflecting light, which colors by reflecting a specific wave length of light, for example, in the visible ray range without requiring any pigment and dye.
2. Description of the Related Art
The type of light energy is roughly classified into: a visible ray that we can generally perceive with our eyes (wave length: 0.38 μm to 0.78 μm); an ultraviolet ray having a shorter wave length than the wave length in the visible ray range (wave length: 0.29 μm to 0.38 μm); and an infrared ray having a longer wave length than the wave length in the visible ray range (wave length: 0.78 μm or longer). The visible ray range is closely related to human visual perception; human eyes perceive the colors of various objects under the visible ray. Generally, the color of an object is generated by absorption of a part of light by the object. The coloring utilizing this principle involves a conventional method using a pigment or a dye, and almost all colorings that can be now found around us are based on this conventional coloring method.
However, such a conventional coloring method is disadvantageous not only in that various pigments or dyes themselves are required but also in that the step of mixing the pigments or dyes, a liquid waste treatment and the like are needed, so that these disadvantages are regarded problems in terms of the manufacturing process and the environment. Further, in view of quality, more than a few drawbacks have been pointed out in that pigments or dyes are eluted on the surface of an object to degrade the texture of the object or in that the designability or commercial value of an object is lost with the degradation of the initial quality of the object based on the faded color due to an ultraviolet ray or the like.
In order to solve the above problems, coloring means utilizing physical actions of light such as interference and diffraction without using so-called colorants such as a pigment and a dye (referred to as structural coloring in a broad sense) has been known. This coloring means achieves the coloring by the interaction between light and the surface of an object or a fine structure within the object. Several methods utilizing such coloring means have been already known in the art.
As a structure utilizing interference and reflection actions of light for achieving the coloring, a material having such a structure that an anisotropically molecular oriented film is sandwiched between two polarizing films to achieve the coloring has been presented (see Journal of THE TEXTILE MACHINERY SOCIETY OF JAPAN, Vol. 42, No. 2, p. 55 (1989) and Vol. 42 No. 10, p. 160 (1989)).
The principle of this coloring is as follows: First, when light from a normal direction is incident on a first polarizing film, the light passing through the first polarizing film is converted to light oscillating only in a fixed direction (linearly polarized light). Second, when the linearly polarized light passes through an anisotropically molecular oriented film which is oriented at 45 degrees, the plane of polarization of light is rotated so that light is converted into elliptically polarized light. Third, when the elliptically polarized light passes through a second polarizing film, the elliptically polarized light is reconverted into linearly polarized light. Then, since the light intensity varies depending on a wave length of light, the linearly polarized light serves as colored polarized light and thus is recognized as a color (i.e., coloring achieved by interference of polarized light).
Moreover, there has also been proposed a material having such a structure that two polymer materials with different refractive indices are alternately deposited to form several tens of layers so as to achieve the coloring (refer to Japanese Patent Application Laid-Open No. H4-295804 and Japanese Patent No. 3036305). The principle of this coloring is as follows: Fresnel reflections, which are caused at the interfaces between alternately deposited layers having different refractive indices, overlap each other to cause interference, resulting in an increase or a decrease in the wave length dependence of a reflectivity or the reflectivity itself. The coloring appears when Fresnel reflections overlap with each other at a specific wave length with a specific phase difference (coloring wave length λ1=2(nada+nbdb): coloring wave length λ1 becomes maximum when optical thicknesses of the respective layers are equal to each other, i.e., nada=nbdb).
Japanese Patent Application Laid-Open No. H4-295804 discloses a film-like reflective polymer material including layers of a first polymer material and a second polymer material having refractive indices different from each other by at least 0.03, which are deposited to a thickness of about 0.1 μm. Further, the inventors of the present invention also disclose, in Japanese Patent No. 3036305, a fibrous coloring structure having a structure in which two polymer materials having different refractive indices are alternately laminated. The coloring fiber disclosed in Japanese Patent No. 3036305 is a non-dyed coloring fiber, changing its color tone depending on the viewing angle. Moreover, when combined with a thread of a particular color, the combined effects of the thread and the fiber permit the coloring fiber to exhibit the texture peculiar to interference.
Meanwhile, as a structure utilizing diffraction and interference actions, a structure having narrow grooves of a constant width on the surface of a fiber to present diffraction and interference colors has been known (refer to Japanese Patent Application Laid-Open No. S62-170512, Japanese Patent Application Laid-Open No. S63-120642, or Japanese Patent Application Laid-Open No. H8-234007). The principle of this coloring is described as follows: when light is incident on an object having a plane or a concave plane on which a large number of grooves in predetermined size (predetermined interval and depth) are regularly formed (as in a so-called diffraction grating), an optical path difference ΔL is generated. When the optical path difference ΔL is equal to an integer multiple of a wave length λ, reflected rays mutually enhance their intensities to increase the brightness (optical path difference ΔL=mλ: where m is a diffraction order, and m=0, 1, 2 . . . ). In practice, incident light at a certain incident angle is provided with the coloring having a wave length λ at a predetermined diffraction angle.